1. Technical Field
The present invention—involving adhesive applicators and adhesive-applicator-equipped bookbinding apparatuses that sheave sequentially supplied sheets, apply adhesive to a sheet sheaf, and then bind a cover sheet onto the sheaf to encase it—relates to improvements in apparatus-internal ambient temperature control in heating a hot-melt adhesive to melt it, applying the molten adhesive to an endface of a sheet sheaf, and cold-hardening the work after encasement.
2. Description of the Related Art
Widely known among bookbinding apparatuses of this type are in general those that automatically form booklets by stacking and sheaving sheets conveyed out from an image-forming or like apparatus, applying adhesive to the spine endface of a sheet sheaf, and then binding onto the sheaf a cover sheet fed from a path that is different from that of the sheaf. Recently in particular, printing systems that on demand form images onto sheets in an image-forming apparatus, sheave the sheets, then bookbinding-finish the sheet sheaves into booklets by binding a cover sheet together with the sheet sheaf are widely being employed.
Examples of this sort of conventional bookbinding apparatus include the machine proposed in FIG. 2 of Japanese Unexamined Pat. App. Pub. No. 2004-114196, which stacks and sheaves onto a tray sheets conveyed out from an image-forming apparatus, applies adhesive to the spine endface of the sheet sheaf, and then binds a cover sheet together with the sheet sheaf and by hardening the adhesive adheres the cover to the sheaf. Then for the adhesive, the machine is configured with a glue container with a built-in applicator roll, and the adhesive in the container is applied to the sheet sheaves with the applicator roll. Chiefly employed in this implementation is a hot-melt adhesive, in which case the adhesive in solid form is charged into the container, and is melted and liquefied with a heating means and spread on with the applicator roll.
The benefits of a hot-melt adhesive—thus with which the adhesive in solid form at ordinary temperatures is heat-liquefied and applied to a sheet sheaf, and adheres by hardening after being applied—are that being in solid form facilitates managing the adhesive during handling and storage, and that during use, because the melted-liquefied adhesive after being applied to a sheet sheaf hardens at a leisurely pace, the cover-sheet binding and related processes can be executed in the interim, expediting bookbinding and its associated processes. On the other hand, problems hot-melt adhesives are known to have are that the adhesives must be kept in a heated/melted state inside the bookbinding apparatus, and that if the latter-stage processes on a sheet sheaf to which adhesive has been applied are not implemented within a predetermined post-application time frame, the adhesive hardens, making it impossible to bind the cover sheet together with the sheet sheaf.
Using hot-melt adhesives widely employed to date in binding, as described above, a sheet sheaf and cover sheet together to form booklets in a bookbinding apparatus leads to the following problems. The fact that the viscosity of a melted/liquefied adhesive will be low when the adhesive temperature is high runs the risk of adhesive applied to a sheaf dripping onto and soiling the cover sheet disposed directly underneath, or soiling the apparatus interior, and in some cases, when in subsequent processes a cover sheet is glued on and spine creases are formed, the adhesive leaks out onto the front and back sides of the cover sheet. Meanwhile, if the adhesive temperature is low, the adhesive will not seep in between leaves of the sheaf, on account of which pages may drop out, or the entire spine-covering area of the cover sheet cannot be glued on uniformly. Inasmuch as any of these problems leads to inferior bookbinding, setting the adhesive temperature to an optimal condition is a crucial issue for bookbinding processes.
Therein, as far as adhesive temperature is concerned, cold hardening in a comparatively short time frame after an adhesive has been applied onto and a cover sheet bound together with sheets is called for. Against this backdrop, attempts have been made, as in the patent reference cited earlier (JP 2004-114196), to optimally control the temperature of the adhesive, yet without taking into consideration the temperature inside the glue-container-outfitted apparatus. Consequently, the apparatus-internal temperature, from its relationship to the high-temperature heat that sheets conveyed out from an image-forming or like apparatus take on, and the heating of the glue container in order to melt the hot-melt adhesive, is predisposed to reach high temperatures. The problem with the apparatus-internal temperature becoming elevated is that, with the temperature of the sheets themselves being raised, applied adhesive drips, or more adhesive than necessary penetrates between the sheaf leaves, inviting faulty bookbinding.
Given these circumstances, the present inventors provided a cooling fan within the housing of an apparatus equipped with a glue container, to attempt to keep the apparatus-internal temperature constant and to promote solidification of the adhesive following sheaf encasement. This resolved problems owing to dripping or excessive inter-sheet permeation of adhesive, with the apparatus-internal temperature having gone high on account of the heat that the sheets themselves have taken on. Nevertheless, cooling the apparatus interior with, for example, a cooling device such as a cooling fan caused adhesive that been applied to a sheet sheaf to cool during the interval when the sheaf is transported to the cover-sheet binding position downstream and is bound together with a cover sheet, and this problem was prohibitive of securely gluing on the cover sheets.